| Hallucination |
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PREVALENCE AND TYPES OF HALLUCINATORY EXPERIENCE Studies have now shown hallucinatory experiences take place across the population world wide. Previous studies, one as early as 1894Sidgwick, H., Johnson, A, Myers, FWH et al (1894) Report on the census of hallucinations. ''Proceedings of the Society for Psychical Research'', 34, 25-394. , have reported that approximately 10% of the population experience hallucinations. A recent survey of over 9,000 people Ohayon MM. (2000) Prevalence of hallucinations and their pathological associations in the general population. ''Psychiatry Research'', 97(2-3), 153-64. reported a much higher figure with almost 39% of people reported hallucinatory experiences, 27% of which reported daytime hallucinations, mostly outside the context of illness or drug use. From this survey, Olfactory (smell) and Gustatory (taste) hallucinations seem the most common in the general population. Hypnagogic Hallucination s and Hypnopompic Hallucination s are considered normal phenomena. Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Auditory hallucinations, particularly of one or more talking voices, are particularly associated with Psychotic disorders such as Schizophrenia , and hold special significance in diagnosing these conditions, although many people not suffering from diagnosable Mental Illness may sometimes hear voices as well.1 The Hearing Voices Movement is a response to the Psychiatric interpretation of auditory hallucination. Other types of auditory hallucinations include musical hallucinations, where people will hear music playing in their mind, usually songs they are familiar with. This can be caused by Lesions on the Brain Stem , occurring most often from Strokes , but also Tumors , sencephalitis, or Abscesses .2 Recent reports have also mentioned that it is possible to get musical hallucinations from listening to music for long periods of time. {Link without Title} Florid hallucinations are usually associated with Drug use (particularly Hallucinogenic Drug s), Sleep Deprivation , psychosis or Neurological Illness . SCIENTIFIC EXPLANATIONS Various theories have been put forward to explain the occurrence of hallucinations. When Psychodynamic ( Freud ian) theories were popular in psychiatry, hallucinations were seen as a projection of unconscious wishes, thoughts and wants. As biological theories have become orthodox, hallucinations are more often thought of (by psychiatrists at least) as being caused by functional deficits in the Brain . With reference to mental illness, the function (or dysfunction) of the Neurotransmitter Dopamine is thought to be particularly important Kapur S. (2003) Psychosis as a state of aberrant salience: a framework linking biology, phenomenology, and pharmacology in schizophrenia. ''American Journal of Psychiatry'', 160(1), 13-23. . s, Memories , Belief s and Thought s). The ability to discriminate between self-generated and external sources of Information is considered to be an important metacognitive skill and one which may break down to cause hallucinatory experiences. Projection of an internal state or a person's own reaction to another may arise in the form of hallucinations, especially auditory hallucinations. A few scientists have argued that such hallucinations may be the result of other conscious thoughts. VISUAL HALLUCINATION SUBTYPES Hypnagogic Hallucination These hallucinations occur just before falling asleep and affect a surprising number of people in the population. The hallucinations can last from seconds to minutes, all the while the subject usually remains aware of the true nature of the images. These are usually associated with Narcolepsy , but can also affect non-narcoleptics. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare. http://brain.oxfordjournals.org/cgi/content/abstract/121/10/1819 Manford and Andermann (1998)] Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Peduncular Hallucinosis Peduncular means pertaining to the . Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Delirium Tremens One of the most enigmatic forms of visual hallucinations are the highly variable, possibly polymodal Delirium Tremens , which is a form of Withdrawal from alcohol in people with late-stage Alcoholism . As the name suggests, the subject is usually agitated and confused, especially in the later stages of this disease. Insight is gradually reduced with the progression of this disorder. Sleep is disturbed and occurs for a shorter period of time, with REM overflow. Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Parkinson's disease and Lewy body Dementia is usually reduced. Parkinson's disease is usually associated with a degraded Substantia Nigra pars compacta, but recent evidence suggests that PD affects a number of sites in the brain. Some places of noted degradation include the median raphe nuclei, the noradrenergic parts of the locus coeruleus and the Cholinergic neurons in the Parabrachial and Pedunculopontine nuclei of the Tegmentum . Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Migraine Coma This type of hallucination is usually experienced during the recovery from a comatose state. The migraine coma can last for up to two days and a state of depression is sometimes comorbid. The hallucinations occur during states of full consciousness and insight into the hallucinatory nature of the images is preserved. It has been noted that ataxic lesions accompany the migraine coma. Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Charles Bonnet Syndrome Charles Bonnet Syndrome is the name given to visual hallucinations experienced by blind patients. The hallucinations can usually be dispersed by opening or closing the eyelids until the visual images disappear. The hallucinations usually occur during the morning or evening, but are not dependent on low light conditions. These prolonged hallucinations usually do not disturb the patients very much as they are aware that they are hallucinating. Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . Focal Epilepsy The visual hallucinations from focal epilepsy are characterized by being brief, and stereotyped. They are usually localized to one part of the visual field and last only a few seconds. Other epileptic features may present themselves between visual episodes. Consciousness is usually impaired in some way, but nevertheless insight into the hallucination is preserved. Usually this type of focal epilepsy is caused by a lesion in the posterior temporoparietal. Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840. . ON TELEVISION AND MOVIES Occasionally television programs and movies let the viewer see hallucinations experienced by one of the characters. For example, an episode of '', Jack Sparrow has hallucinations, seeing a crew made up entirely out of copies of himself. Another case occurs in Melrose Place , when Dr Kimberely Shaw saw visions of a non-existent personality constantly. This hallucination was caused by a tumor pressing against her brain. On Ally McBeal , the Main Character frequently has a hallucination of a Dancing Baby , due to the fact that as she gets older, her Biological Clock ticks faster. These examples are four out of millions. SEE ALSO
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